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Old 07-29-2009, 05:04 PM   #1
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joist sistering to support clawfoot tub


I want to put a clawfoot in an 2nd floor bathroom of a 1903 built Victoria. The bathroom is only 8' long but the span of the joists is 11 or 12', 2x10 joists 16oc.

If I sister the joists only the 8' length of the bathroom, with one end on the outside wall and the other supported by nothing, does this do any good or just add weight? Thank you!

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Old 07-29-2009, 10:53 PM   #2
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joist sistering to support clawfoot tub


Hi JR,

Assuming the joists is not rotted near the end not being sistered, your plan will help to reduce deflection, but will not increase the total weight the system can tolerate as a whole. However the greatest point of stress is towards the center of the span, so even if you sister only the mid-2/3 of the span you will improve its strength. For a joist to crack 2-3 ft. from its support is unlikely.

I guess the entire length of the span is not accessible? How about if you sister with 2x8 or even 2x6's?

Jaz

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Old 07-30-2009, 12:45 AM   #3
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joist sistering to support clawfoot tub


Thanks Jazman, but I am confused. If sistering less than the entire length of the span won't help increase the load the joists can bear, then how is sistering the middle 2/3 going to make them stronger?

Are you suggesting using a smaller size joist so I can slide them into the inaccessible parts of the span? I wouldn't be able to fasten them to anything past the 8' width of the bathroom...
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Old 07-30-2009, 11:49 PM   #4
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joist sistering to support clawfoot tub


By sistering even part of the span you will stiffen the joists as you know. The dead weight rating in combo with the deflection rating is what you need to improve, no fear of cracking the joists altogether.

Sometimes it is difficult or impossible to sister with equal size lumber, so yes, even smaller joists will help. Are you doing the work from below or from inside the room?

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Old 07-31-2009, 12:28 AM   #5
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joist sistering to support clawfoot tub


I'm doing it from inside the room. Now that the demo is complete I see I'll only be able to do the 5' of sistering. You're saying this will improve the strenth of the floor and the load it can bear?

Will blocking further improve this?
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Old 07-31-2009, 11:45 PM   #6
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joist sistering to support clawfoot tub


Yes, all those things will help. Also add some X bracing wherever possible. The sistering will stiffen the center making the entire joists stiffer. The ends not sistered will become the "weak link" of the system. However, you will not break the joists unless you add tons of weight cuz the single joists span only a few feet.

Any doubts, hire a structural engineer to verify.

Jaz

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